History of the Franklin Mine

by John Leach Baum

The outcrop of the Franklin zinc-iron-manganese ore body was known from the earliest days because a portion of the deposit was exposed at the surface. Attempts to smelt the ore for iron in the local blast furnace used on the adjacent magnetite ore were futile. Early transfer of the property in order were King Charles II of England, to his brother James Duke of York, to Sir George Carteret, at inheritance tax sale to William Penn and eleven partners who founded an ownership association called the Board of Proprietors which subsequently sold to Anthony Sharp in 1750. In 1810 heir Edward Sharp sold to Dr. Samuel Fowler and a partner (soon bought out Franklin Mine Hill, site of the Franklin ore body. It was Dr. Sam who brought the property to the attention of science. His son, Colonel Samuel Fowler, acquired both the Franklin and Sterling properties to initiate the ultimate development of the deposits.

In 1810 the zinc content of zincite was published. The zinc minerals zincite, franklinite, and willemite being unique, many years of experimentation were to pass before their metal content could be removed. Zinc oxide was the first product and the ancestral Zinc Company the first to manufacture ready-mixed paint. This was promoted as a superior replacement for poisonous lead-based paint, which even today is an environmental hazard.

Due to unfortunate division of property titles based on poor understanding of the nature of the ores and their occurrence, there were numerous mining companies working the Franklin outcrop. Legal challenges among the operators were so divisive that in 1897 all properties were combined and reorganization produced an increasingly successful venture under the title of the New Jersey Zinc Company. Additional favorable factors were the development of the ore into franklinite and willemite-zincite fractions and development of a mining method designed to effectuate total recovery of the ore reserves.

Efficient operation of the consolidated property required a new mill or concentrating plant, a revised mining method with relocated shafts and a new town, complete with such services would make Franklin a model mining community. To effect many of these improvements, Robert Catlin, a prominent mining engineer, was enticed to Franklin. He imported the finest mining talent, much of it from Eastern Europe and Cornwall, England. As a result of the richness of the ore, nearly 20% zinc with substantial recovery of iron and manganese, and the dedication of management and workers, the venture was a complete success.

Due to the ore body being essentially a steeply inclined slab, the mining method selected was calculated to allow the overhanging wallrock to subside under controlled conditions. Thus the orebody was divided into vertical segments across the width of the ore and then alternate segments were mined out from the bottom up. Each worked-out area or stope was filled with the mill reject and remaining support slabs, called "pillars", were mined downward in ten foot high slices, encouraging the overlying barren rock, called "the hanging wall", to slump. Since much timber was used in pillar support while mining, and a plank floor was laid just before the horizontal slice was advanced, collapse of the timber supports upon the floor allowed the overlying jumble of timber and planks fill added from above to cushion the controlled subsidence of the hanging wall and provided a plank ceiling for the next slice to be mined below. In this manner, essentially the entire ore body was recovered.

Concentration of the ore was important to enable a number of different products at the Palmerton, Pennsylvania, smelters and all Franklin ore was so treated. The magnetic concentration of franklinite was mixed with anthracite coal and roasted to recover much of the zinc oxide and the residue was smelted to produce an iron-manganese alloy called spiegleisen, used in the manufacture of manganese steel. The willemite-zincite mill product was also mixed with anthracite coal and smelted in the absence of air to produce a zinc gas, which condensed into zinc metal. A great pile of waste resulted.

Initially an ore body of limited value, Franklin Mine Hill became a bonanza, producing a half billion dollars worth of zinc over a period of 106 years. Obstacles to success were enormous, but each was overcome by talented men who wrote nationally-important mining law, developed markets for the first ready-mix zinc oxide paint to replace lead paint, invented the zinc die casting business and created the alloys that made it possible, devised a mining method to recover all the Franklin ore body and perfected concentration and smelting of unique ores. Mining of the Franklin ore body was terminated on September 30, 1954.

In some respects, the history of the Franklin ore is the history of American mineralogy. Starting with the first described mineral for the United States, zincite, by Dr. Archibald Bruce in 1810, subsequently hundreds of species have been found here, many new to science and some unique to the locality. The science of mineralogy has benefited immeasurably from the study of this great deposit. Concurrently with these studies and contributing to them, collecting mineral specimens continues. Closing of the mines has limited somewhat the availability of good specimens in quantity, but collections become available with time and trophy specimens of rare or crystallized or spectacular fluorescent species bring ever higher prices.